The present invention relates to methods and apparatus for cleaning particulate contamination from a moving substrate surface; more particularly, to methods and apparatus for traversing a contact cleaning roller axially while rolling along a moving substrate to transfer contaminant particles from the moving substrate to the contact cleaning roller; and most particularly, to methods and apparatus for progressively and continuously cleaning a contact cleaning roller while the roller itself is continuously cleaning a moving substrate.
In many manufacturing processes involving substrates, for example, in continuous-web printing and in the coating of photographic films and papers, particulate contamination of the substrate surface can lead to reduced quality of the coated product and to increased waste. It is known to use a polymer-covered roller in rolling contact with a planar substrate to remove particles from the surface of the planar substrate ahead of the printing or coating point. It is also known to use a polymer-covered roller in rolling contact with another roller, for example, a process roller such as another contact cleaning roller, calendar roller, offset printing roller, and the like. The surface of such a polymer-covered roller (known in the art as a contact cleaning roller and also referred to herein as a CCR), may comprise a polymer having a high surface energy, for example, polyurethane or silicone rubber, or alternatively, a polymer exhibiting adhesive tack, such as any of the well-known tape adhesives. The CCR surface exhibits a greater attraction for particles than does the substrate surface, so that particles are transferred from the substrate to the CCR at the point of rolling contact.
A CCR may itself function as a conveyance roller, for example, in a string of web conveyance rollers, in which use the CCR may enjoy a substantial angle of wrap of the web, for example, a wrap angle of 90xc2x0 or even greater. A conveyance roller as used herein is a roller whose position defines a portion of a web conveyance path. Such engagement by a CCR may be on either side of the web being conveyed. See, for example, U.S. Pat. No. 5,251,348 issued Oct. 12, 1993 to Corrado et al. A CCR may also function as a non-conveyance roller, that is, the web conveyance path is not a function of the presence or absence of the CCR. In such use, a CCR typically is positioned as a nip roller urged against a non-CCR conveyance roller (backing roller), the web passing therebetween, whereby the web is conveyed on a first or back side against the conveyance roller and is cleaned on a second or front side by the CCR. See, for example, U.S. Pat. No. 5,611,281 (""281) issued Mar. 18, 1997 to Corrado et al. which is hereby incorporated by reference.
Many substrates, for example, web substrates, have particulate contamination concentrated along the outer edges of the substrate surface which can lead to premature clogging and failure of a full-width CCR while more central portions of the CCR surface are still non-clogged and serviceable. The U.S. Pat. No. 5,611,281 discloses to prolong the useful life of a CCR between renewals (removal of accumulated particles) by oscillating the CCR axially a short distance while it is rolling along the substrate surface, thereby causing accumulating particles to be distributed as a broad band over a substantial portion of the axial length of the roller along each substrate edge.
Through use, the surface of a CCR becomes progressively clogged with removed particles and progressively loses cleaning effectiveness. Cleaning, also known as renewal, of a CCR surface may be accomplished through washing, for example, as disclosed in U.S. Pat. Nos. 5,275,104 and 5,611,281, wherein a plurality of CCR""s are alternably provided such that continuous cleaning of the substrate surface can be maintained by a fresh CCR while each CCR in turn is rotated out of service for off-line renewal, including drying. This is necessary in the prior art because washing of a CCR while in service against a substrate risks undesirable transfer of cleaning fluid onto the substrate. Such a multiple-CCR installation is complex and costly to build and to maintain.
Alternatively, as disclosed in the ""281 patent, a higher-tack, or secondary, CCR may be engaged to clean particles from a lower-tack, or primary, CCR (which procedure is defined hereby as secondary cleaning) which itself has cleaned, or is actively cleaning, particles from some other substrate surface such as a web or another process roller (which procedure is defined hereby as primary cleaning). For continuous primary cleaning, this arrangement requires continuous contact of the primary CCR with the substrate. Thus, a problem arises as to how to clean or renew the secondary CCR without reverse-contaminating the primary CCR and, indirectly, the substrate being cleaned.
Typically, a secondary CCR, like a primary CCR, comprises a solid polymer covered roller or a length of adhesive tape wound on a core with the adhesive surface facing outwards. In the prior art, renewal of the secondary CCR requires first that the roller be retracted from contact with the primary CCR to avoid contamination thereof and replaced in its cleaning function by another secondary CCR. A secondary CCR may then be washed automatically offline, as referenced above, or manually by an operator, either in place or after being removed to a washing station. A tape-type secondary CCR is renewed either by unwinding and discarding the exposed tape to present a fresh convolution or by replacing the roll of tape when spent, as disclosed in U.S. Pat. No. 4,009,047. In such a prior art application, at least two alternable secondary CCR""s are required, at an increase in expense and complexity.
Thus there is a need for a method and apparatus for providing online renewal cleaning of a CCR, either primary or secondary, which permits regular renewal of the CCR without requiring any additional or replacement CCR""s and without endangering the substrate being cleaned.
It is a principal object of the invention to provide an improved method and apparatus for safe, inexpensive, simple, and frequent renewal of a primary and/or secondary CCR while performing its online cleaning function.
It is a further object of the invention to provide an improved method and apparatus for continuous cleaning of a substrate by a single CCR.
Briefly described, a system for cleaning a moving substrate includes a contact cleaning roller and translating means for axially oscillating the CCR, such as a carriage on a rail mounted adjacent to the substrate surface and substantially transverse to the direction of movement thereof, while in rolling contact with the substrate surface, substantially as disclosed in Patent ""281. Two renewal stations for cleaning the CCR are mounted adjacent the rail, one station being mounted outboard of each longitudinal edge of the substrate. The CCR is at least twice as long as the width of the substrate and is in renewal contact with at least one of the renewal stations at all times. The CCR is axially oscillable for a distance sufficient that all portions of the CCR surface are cleaned by the renewal stations in combination during one oscillation cycle of the CCR while the CCR maintains continuous contact across the full width of the substrate. In a preferred method, the cleaning station is engaged with the CCR for renewal during the outward stroke of the CCR past the station and is retracted during the inward stroke, although the station may also be left in contact with the CCR during the inward stroke if so desired. Generally, this is not necessary.
Thus, a single CCR may be continuously cleaned without being pivoted out of contact with the substrate and without risk of contamination to the substrate as in the prior art.
In a first preferred embodiment, a contact cleaning roller mounted on the carriage is a primary CCR and the substrate is an object such as a continuous flexible web or rigid sheet to be cleaned by the apparatus and method of the system.
In a second preferred embodiment, a contact cleaning roller mounted on the carriage is a secondary CCR and the substrate is a primary CCR for cleaning an object such as a web. The primary CCR is positionable to be in contact with a surface of a substrate to be cleaned and may also be positionable to be out of contact with the substrate surface as desired. The primary CCR preferably is axially fixed and in length is of the order of the width of the substrate. The secondary CCR may be moved axially along the surface of the primary CCR either in contact or out of contact therewith.
Two substantially identical CCR cleaning systems in accordance with the invention may be disposed on opposite sides of a substrate to clean both sides in a single pass of the substrate through the apparatus.